1. Field of the Invention
The present invention relates to an improvement in a preassembled, molded, disposable intraoral dam for use during dental procedures, the improvement comprising a solution-grade thermoplastic polyurethane composition, which, while retaining the physical properties of natural rubber, latex and other elastomeric intraoral dams, has the added benefit of being impermeable to particles as small as 10 micrometers, hemocompatible, non-cytotoxic, with enhanced puncture and tear resistance, and high tensile strength; in addition, it remains flexible at body temperature without losing its elasticity or strength.
2. The Prior Art
The claimed improvement is a solution-grade thermoplastic polyurethane intraoral dam which comprises a unitary preassembled elastic membrane held taut about the periphery by a complementary annular spring-like frame member, as disclosed in U.S. Pat. No. 4,828,491, May 9, 1989. One of the most undesirable qualities of prior art elastomeric intraoral dams results from pinholes which may occur as a result of the molecular composition of natural vulcanized rubber, and the latex rubber manufacturing process. These pinholes are shown by electron microscopy and X-ray analysis to be large enough (i.e., up to 15 micrometers wide, and up to 30 micrometers deep, in some cases) to allow the transmission of disease-producing pathogens. These studies further show that irregular particles are noted to be deeply embedded in the surface of the elastomer, producing a pitted structure. Other undesirable qualities of elastomers used in prior art intraoral dams include hyperallergic reactions, loss of elastic properties at body temperature, and inadequate puncture and tear resistance. Consequently, while elastomeric intraoral dams of the prior art do tend to provide a limited sterile operative field, it is clear that an intraoral dam produced from an elastomeric product which eliminates the undesirable qualities, as outlined above, is needed in the art. The claimed improvement insures a significantly greater guarantee of a sterile operative field for oral procedures by effectively eliminating the drawbacks encountered in prior art intraoral dams using natural rubber and latex materials.
Of the prior art relating to extrudable thermoplastic polyurethanes for clinical uses, that which is most germane to the claimed improvement is U.S. Pat. No. 4,523,005, June 11, 1985, which teaches an extrudable polyurethane which is the reaction product of an aliphatic organic diisocyanate, a high molecular weight polyether polyol, and 1,4 butane diol. However, this reference only contemplates an extruded polyurethane, and neither suggests nor anticipates solution dipping procedures, as is employed in the claimed improvement. This prior art polyurethane is disclosed in the context of catheters, blood bags, and surgical tubings, and does not suggest any properties of the polymer in films having a thickness suitable for the formation of the intraoral dam of the claimed improvement. Other related patents by the same inventor (Szycher) include U.S. Pat. No. 4,614,787, which discloses a drug dispensing system which uses a polyurethane matrix which is the reaction product of an isocyanate terminated prepolymer and a monomer containing hydroxyl and vinyl groups; U.S. Pat. No. 4,483,759 discloses a flexible elastomeric polyurethane acrylic copolymer which is radiation cured; and U.S. Pat. No. 4,638,043, which discloses a drug releasing system comprising a polyurethane acrylic copolymer which is the reaction product of an oligomer of a diisocyanate, a glycol with molecular weight between the range of 500-5000, and an acrylyl chain terminator, with molecular weight between the range of 40-200, molecular weight units being cured by actinic radiation. These related patents are included as part of the disclosure for informational purposes only, and are not germane to the claimed improvement, as the impact is merely cumulative.
U.S. Pat. No. 4,000,117, Dec. 28, 1976, also discloses a solution-grade thermoplastic polyurethane elastomer. However, this disclosure teaches a polyester-based urethane polymer, while the claimed improvement is a polyether-based urethane, with materially different properties, including greater tensile strength and ultimate elongation before breakage, higher flex fatigue and hydrolytic stability. In addition, the polyether urethane of the claimed improvement shows no degradation in properties over substantial aging periods, either natural or accelerated, while the polyester urethanes disclosed in U.S. Pat. No. 4,000,117 show substantial and immediate degradation of properties on aging.
U.S. Pat. No. 4,463,156, July 31, 1989, discloses a cross-linked, thermoset polyurethane, and is therefore outside the scope of the claimed improvement, which is directed to a thermoplastic polyurethane.